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><H1
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NAME="SQL-SET-CONSTRAINTS"
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>SET CONSTRAINTS</H1
><DIV
CLASS="REFNAMEDIV"
><A
NAME="AEN75507"
></A
><H2
>Name</H2
>SET CONSTRAINTS&nbsp;--&nbsp;set constraint check timing for the current transaction</DIV
><DIV
CLASS="REFSYNOPSISDIV"
><A
NAME="AEN75512"
></A
><H2
>Synopsis</H2
><PRE
CLASS="SYNOPSIS"
>SET CONSTRAINTS { ALL | <TT
CLASS="REPLACEABLE"
><I
>name</I
></TT
> [, ...] } { DEFERRED | IMMEDIATE }</PRE
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN75515"
></A
><H2
>Description</H2
><P
>   <TT
CLASS="COMMAND"
>SET CONSTRAINTS</TT
> sets the behavior of constraint
   checking within the current transaction. <TT
CLASS="LITERAL"
>IMMEDIATE</TT
>
   constraints are checked at the end of each
   statement. <TT
CLASS="LITERAL"
>DEFERRED</TT
> constraints are not checked until
   transaction commit.  Each constraint has its own
   <TT
CLASS="LITERAL"
>IMMEDIATE</TT
> or <TT
CLASS="LITERAL"
>DEFERRED</TT
> mode.
  </P
><P
>   Upon creation, a constraint is given one of three
   characteristics: <TT
CLASS="LITERAL"
>DEFERRABLE INITIALLY DEFERRED</TT
>,
   <TT
CLASS="LITERAL"
>DEFERRABLE INITIALLY IMMEDIATE</TT
>, or
   <TT
CLASS="LITERAL"
>NOT DEFERRABLE</TT
>. The third
   class is always <TT
CLASS="LITERAL"
>IMMEDIATE</TT
> and is not affected by the
   <TT
CLASS="COMMAND"
>SET CONSTRAINTS</TT
> command.  The first two classes start
   every transaction in the indicated mode, but their behavior can be changed
   within a transaction by <TT
CLASS="COMMAND"
>SET CONSTRAINTS</TT
>.
  </P
><P
>   <TT
CLASS="COMMAND"
>SET CONSTRAINTS</TT
> with a list of constraint names changes
   the mode of just those constraints (which must all be deferrable).  Each
   constraint name can be schema-qualified.  The
   current schema search path is used to find the first matching name if
   no schema name is specified.  <TT
CLASS="COMMAND"
>SET CONSTRAINTS ALL</TT
>
   changes the mode of all deferrable constraints.
  </P
><P
>   When <TT
CLASS="COMMAND"
>SET CONSTRAINTS</TT
> changes the mode of a constraint
   from <TT
CLASS="LITERAL"
>DEFERRED</TT
>
   to <TT
CLASS="LITERAL"
>IMMEDIATE</TT
>, the new mode takes effect
   retroactively: any outstanding data modifications that would have
   been checked at the end of the transaction are instead checked during the
   execution of the <TT
CLASS="COMMAND"
>SET CONSTRAINTS</TT
> command.
   If any such constraint is violated, the <TT
CLASS="COMMAND"
>SET CONSTRAINTS</TT
>
   fails (and does not change the constraint mode).  Thus, <TT
CLASS="COMMAND"
>SET
   CONSTRAINTS</TT
> can be used to force checking of constraints to
   occur at a specific point in a transaction.
  </P
><P
>   Currently, only <TT
CLASS="LITERAL"
>UNIQUE</TT
>, <TT
CLASS="LITERAL"
>PRIMARY KEY</TT
>,
   <TT
CLASS="LITERAL"
>REFERENCES</TT
> (foreign key), and <TT
CLASS="LITERAL"
>EXCLUDE</TT
>
   constraints are affected by this setting.
   <TT
CLASS="LITERAL"
>NOT NULL</TT
> and <TT
CLASS="LITERAL"
>CHECK</TT
> constraints are
   always checked immediately when a row is inserted or modified
   (<SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>not</I
></SPAN
> at the end of the statement).
   Uniqueness and exclusion constraints that have not been declared
   <TT
CLASS="LITERAL"
>DEFERRABLE</TT
> are also checked immediately.
  </P
><P
>   The firing of triggers that are declared as <SPAN
CLASS="QUOTE"
>"constraint triggers"</SPAN
>
   is also controlled by this setting &mdash; they fire at the same time
   that the associated constraint should be checked.
  </P
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN75551"
></A
><H2
>Notes</H2
><P
>   Because <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> does not require constraint
   names to be unique within a schema (but only per-table), it is possible
   that there is more than one match for a specified constraint name.
   In this case <TT
CLASS="COMMAND"
>SET CONSTRAINTS</TT
> will act on all matches.
   For a non-schema-qualified name, once a match or matches have been found in
   some schema in the search path, schemas appearing later in the path are not
   searched.
  </P
><P
>   This command only alters the behavior of constraints within the
   current transaction. Thus, if you execute this command outside of a
   transaction block
   (<TT
CLASS="COMMAND"
>BEGIN</TT
>/<TT
CLASS="COMMAND"
>COMMIT</TT
> pair), it will
   not appear to have any effect.
  </P
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN75559"
></A
><H2
>Compatibility</H2
><P
>   This command complies with the behavior defined in the SQL
   standard, except for the limitation that, in
   <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
>, it does not apply to
   <TT
CLASS="LITERAL"
>NOT NULL</TT
> and <TT
CLASS="LITERAL"
>CHECK</TT
> constraints.
   Also, <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> checks non-deferrable
   uniqueness constraints immediately, not at end of statement as the
   standard would suggest.
  </P
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